*{
    margin: 0;
    padding: 0;
    text-decoration: none;
    list-style: none;
    box-sizing: border-box;
}
.box{
    width: 500px;
    height: 500px;
    margin: auto;   
    border: 1px solid red;
}
button{
    width: 100px;
    display: block;
    margin-left: 50px;
}
.showimg{
    width: 200px;
    height: 200px;
    border: 1px solid red;
    margin: auto;
}

.showimg img {
    width: 200px;
    height: 200px;
}